Milling behaviour is problematic when using hydroacoustics to estimate the
number of migrating fish in rivers. Milling behaviour was observed for adult
sockeye salmon migrating upstream in the Wannock River, to their spawning
grounds in the tributaries of Owikeno Lake in the central coast area of
British Columbia, Canada. We classified the acoustic salmon tracks to
separate the milling fish from the actively migrating fish in an attempt to
obtain an estimate of sockeye salmon flux as they migrate to their spawning
grounds. We used discriminant function analysis and found that three
variables measured on each track were sufficient for the classification of
the acoustic tracks into milling and non-milling categories with an
approximate classification accuracy of 98%. The method we present can
also be used to separate tracks of targets of interest from noise or debris
tracks that occur in the acoustic data, if discrete track characteristics
are ascertained.